The present invention relates to a blow lance for treating molten metal in metallurgical vessels, consisting of a metal tube provided with refractory ceramic lining.
In the course of the development of metallurgy, and as a result of the efforts to increase the dimensions, capacity and specific output of the metallurgical installations, several steel treatments outside the vessels have been developed during the last decade. These processes are used particularly for deoxidation and desulfurization of the steels.
The idea of admitting the powdery materials into the molten metal resulted from the efforts aimed at the saving of material, as well as at the more efficient execution of the process, but certain technological functions can be carried out only this way in the practice.
The admission of such powder, or granular materials into the molten bath takes place with the aid of injection systems.
The injection systems include a blow lance for injecting various gases and /in given cases powdery or granular agents/ below the surface of the melt.
The known blow lances generally consist of a thick-walled copper tube provided with refractory lining.
In the course of producing the so-called once-operated lance type, a self-setting fireproof composition is applied onto the surface of the copper tube, then tube pieces similarly made of refractory clay, generally of chamotte are pulled over the composition. This is followed again by the application of fireproof composition and by drying of the lining.
The multi-operated lances are produced in such a manner, that liquid refractory clay containing over 80% Al.sub.2 O.sub.3 is poured over the copper tube, then it is baked.
The fundamental disadvantage of both lance types is that they are extremely rigid and brittle, which frequently leads to failure during operation. Namely the hot molten metal is never in static condition, the immersed lance is set into vibration, thus cracks appear on the lining, after which the lance becomes useless with a fairly short time.
The considerable difference between the coefficients of thermal expansion of the thick-walled copper tube and the lining results similarly in a tendency to crack. Since the two layers are in contact with each other, and they become fairly hot during immersion into the hot molten metal, cracks appear merely as a result of the difference between the coefficients of thermal expansion.
Further difficulty is due to the intensive heating of the blow lances, since the temperature of the molten metals exceeds substantially 1000.degree. C.